1. Technical Field
The present invention relates to a silicon-based optical subassembly and, more particularly, to an optical subassembly including a silicon substrate with a plurality of etched openings for positioning of various optical components.
2. Description of the Prior Art
Semiconductor optical devices such as lasers are used in a wide variety of applications, due to their compactness, relatively high efficiency, and well-controlled output. However, a number of requirements are imposed upon these devices. For durability, cooling of the optical device is often necessary, since prolonged high temperature operation can seriously damage and even destroy the device. Further, since the output light intensity from the device is a function of its junction temperature, the supporting structure must be able to efficiently dissipate the heat generated by the high current density in the device in its operating state.
As is well-known in the art of laser packaging, many optical subassemblies utilize a thermoelectric cooler (TEC) to control the laser's operating temperature with respect to the ambient temperature inside the package. In applications which utilize an internal optical isolator, ambient temperature fluctuations have been found to also affect the isolator's optical component (e.g., Faraday rotator material), resulting in changes in the amount of isolation achieved as a function of temperature. The temperature of the isolator optical component may be controlled. However, in these arrangements, the isolator's magnet is usually (unnecessarily) cooled, thus increasing the work required of the thermoelectric cooler and perhaps adversely affecting its performance. The result is a measure of uncertainty in the amount of isolation a package will yield.
Issues regarding the assembly of these semiconductor optical devices with the required lensing and other passive optical components is another area of concern. In most conventional optical subassemblies, the supporting structure may comprise a number of different members. For example, a conventional optical subassembly may utilize one member for the active (e.g., laser) device and a separate member for the passive components. Alignment between the two members is thus required to achieve the desired minimum level of acceptable coupling loss. Alternatively, a single mounting member may be used to hold all the required optical components. In the latter arrangement, each mounting member is individually formed, using precision die-cast piece parts, for example. Additionally, active alignment operations are often required as each component is affixed to the mounting member. As a result, the optical subassembly is often a relatively expensive component of a lightwave transmitter, requiring a relatively long, expensive and tedious assembly process. Further, any modifications in the size, number or arrangement of the optical components often necessitates a redesign of the complete optical subassembly.
Thus, a need remains in the prior art for an optical subassembly which is robust in design, relatively simple to assemble (i.e., requiring few, if any, active alignments), and more amenable to high-volume, low-cost manufacture than those available in the prior art. Further, a need remains for an optical subassembly, including an isolator, which is capable of efficiently controlling the temperature of both the laser and the isolator.